Will and George had 60 marbles in total. Will had 20 marbles less than George at first. After Will and George played a game with Kathy, Will had ¹₅ as many marbles as George. If Will lost as many marbles as George to Kathy, find the number of marbles that George lost to Kathy.

	Will	George	Difference
Before	1 u	1 u + 20	20
Change	- ?	- ?
After	1 p	5 p	4 p

Total number of marbles at first
= 1 u + 1 u + 20 
= 2 u + 20

2 u + 20 = 60
2 u = 60 - 20
2 u = 40

1 u = 40 ÷ 2 = 20

Since Will lost the same number of marbles as George, the difference in the number of marbles between Will and George at first and in the end remains the same.

Difference in the number of marbles in the end
= 5 p - 1 p
= 4 p

4 p = 20

1 p = 20 ÷ 4 = 5

Number of marbles that Will lost to Kathy
= 1 u - 1 p
= 20 - 1 x 5
= 20 - 5
= 15

Since George lost the same number of marbles as Will, the number of marbles that each lost to Kathy is the same.

Number of marbles that George lost = 15

Answer(s): 15